Magnets have been used in many machines and tools around us, such as various kinds of motors, and recently, the dimensions and weight of these machines and tools have been reduced, and the efficiency thereof has been enhanced. Accordingly, the development of permanent magnets exhibiting higher power has been demanded. To meet such demand, RFeB-based magnets (rare earth magnets), each being composed of rare earth elements (R), boron (B) and iron (Fe), have been developed. Examples of the methods for manufacturing such rare earth magnets include a melt-spinning method as one rapid-quenching method, which is disclosed in patent documents 1 and 2. And, as disclosed in patent documents 3 and 4, examples of such methods include HDDR (hydrogenation-disproportion-desorption-recombination) methods in which a hydrogenation·disproportionation reaction is carried out in two processes basically composed of a hydrogenation process and a dehydrogenation process. With these conventional methods, however, only magnet powder exhibiting low magnetic properties can be obtained. And these conventional methods are difficult to suit to the mass production of anisotropic magnet powder exhibiting excellent magnetic properties.
The present inventors have already developed a method for manufacturing anisotropic magnet powder exhibiting excellent magnetic properties, which is different from the above-described conventional methods. The properties of the magnet powder obtained with this method are unique, and accordingly, this method greatly differs from the HDDR method in processes thereof, whereby this method is called the d-HDDR method to distinguish it from the HDDR method. This d-HDDR method is characterized in that a plurality of processes using different temperatures and hydrogen pressures are provided, and that the reaction of the RFeB-based alloy and hydrogen is adjusted to a slow rate to obtain a homogeneous anisotropic magnet powder exhibiting excellent magnetic properties. More specifically, the d-HDDR method is basically composed of four processes consisting of a low-temperature hydrogenation process in which the RFeB-based alloy is made to absorb hydrogen sufficiently at room temperature, a high-temperature hydrogenation process in which a hydrogenation·disproportionation reaction is made under a low hydrogen pressure, a first evacuation process in which hydrogen is made to dissociate slowly under a hydrogen pressure as high as possible, and a second evacuation process in which hydrogen is removed from a resultant material. The details of each process are disclosed in patent documents 5 and 6, and non-patent document 1, etc.
Patent document 1: U.S. Pat. No. 4,851,058
Patent document 2: U.S. Pat. No. 5,411,608
Patent document 3: Publication of unexamined JP patent application No. Hei2-4901
Patent document 4: Publication of unexamined JP patent application No. Hei11-31610
Patent document 5: Japanese Patent No. 3250551
Patent document 6: Publication of unexamined JP patent application No. 2002-93610
Non-patent document 1: Transactions of the Magnetics Society of Japan, 24(2000), P. 407